The present invention relates to a deceleration control device for a vehicle, which detects deceleration of the vehicle so as to control the deceleration to a target deceleration, for example, a deceleration control device for a vehicle of unmanned operation, which runs in a predetermined acceleration and deceleration pattern or whose acceleration and deceleration are subjected to remote control or computer control, a deceleration control device for avoiding collision between a vehicle and a preceding vehicle from distance between the vehicle and the preceding vehicle and speed of the vehicle and a deceleration control device which is capable of keeping deceleration due to stepping stroke or stepping force of a brake pedal, constant irrespective of weight of a vehicle, wear of brake pads, etc.
In a prior art deceleration control device for a vehicle, relation between brake fluid pressure and deceleration is stored, as a map, in a memory and a brake fluid pressure corresponding to a target deceleration is read out of the memory such that brake fluid pressure is set to the value read out of the memory.
Japanese Patent Laid-Open Publication No. 5-105045 (1993) discloses a method of controlling deceleration of a vehicle in a system for preventing bump of the vehicle against a preceding motor vehicle from behind. In the deceleration control method of this prior art document, decelerations, which represent accelerations or decelerations of the vehicle, are calculated from a plurality of sensors composed of acceleration or deceleration sensors, etc. Even when speed of the vehicle is low, deceleration closer to an actual value is obtained by taking a variance mean of the decelerations calculated from the sensors, so that hydraulic pressure of a hydraulic brake can be controlled accurately and thus, impact prior to stop of the vehicle can be lessened.
Meanwhile, in known deceleration control devices, in case various detection means necessary for deceleration control, e.g., a speed detection means and an acceleration or deceleration detection means fail, safety is secured by prohibiting deceleration control.
However, when speed of the vehicle is low, it is difficult to accurately calculate deceleration of the vehicle. In order to solve this problem, the prior art document referred to above teaches that the variance mean of the decelerations calculated from the sensors is taken. However, such a problem arises that calculation for taking the variance mean lays a rather heavy burden on a microcomputer. Meanwhile, when speed of the vehicle is low, brake fluid pressure is replaced with deceleration from predetermined relation between brake fluid pressure and deceleration of the vehicle. However, the predetermined relation between brake fluid pressure and deceleration of the vehicle varies according to changes of characteristics of a brake system due to wear of tires, wear of brake pads, etc. Thus, if relation between brake fluid pressure and deceleration of the vehicle is merely stored, as the map, in the memory initially, the relation changes with time disadvantageously.
Furthermore, if deceleration control is prohibited in an unmanned vehicle when various detection means necessary for deceleration control, e.g., a speed detection means and an acceleration or deceleration detection means fail, there is no means for stopping the vehicle. In order to solve this problem, a preliminary stop means is required to be provided additionally.